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Friday, July 29, 2016

Xpwr 3910__ Building The Psycho Killer MXS

Extreme aerobatics have changed radically since I started in 2006. The planes have gotten lighter, stronger, sleeker, faster and much more powerful. We have seen several evolutions in design and equipment, and even some of the older planes have benefitted from evolution in servo and power systems technology.

When The Boss and Ben Fisher merged Extreme Flight and 3DHS into one monster company, we knew good things would be coming. Those two have advanced the state of the art so much independently that together there is not going to be any stopping them, and with what we've seen so far, no one else is even going to be able to keep up. It took them some time to set things up and the new products streaming out, and that has only just begun.

The Psycho Killer MXS
The Extreme Flight MXS EXP is one of my more beloved airframes. It was my second EXP, and much different than anything else I had flown at the time. It was a new challenge at a time when I really needed one, and of course, I really liked the plane too. It was stable, so I could push it hard, but it was also really agile, so I had to open my own envelope to take advantage of that.

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I also survived a heart attack flying one, and I spent a lot of time in the hospital (partially because there was nothing else to do) thinking about the MXS, how to improve my set up and get the most out of the plane. In a lot of ways, the MXS was the motivation for getting off the couch and back into the game so quickly, and greatly helped my recovery. As much as I love everything about the plane, this will probably always be the thing I hold most dear about it.

Previously the MXS was such a wigged out plane that it never occurred to me it could be possible to make it even more badass. The MXS will be going on six years old this October, and equipment has improved so much it has become time to update my set up and take advantage of that.

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Some of you may remember earlier this year when I built a special Extra SHP with Hitec HV servos, double ball link hardware, and generally every trick have learned from eight years of flying that plane, and using the new tricked out HS5070MH servos. It was the most hot-rodded SHP ever built, and thus earning itself the name "Murder SHP." Since the SHP is such a darling little sweetheart of a plane with gentle manners and subline stability, going crazy with the set up only went so far. Certainly it's a nice plane, deadly capable, in fact. However, it made me wonder what could be done with a plane that was wild to start with, and the king of wild is the MXS.

With the introduction of the new XPWR 3810 motor, we can now run a bigger 14/8 propeller and take advantage of the added thrust and airflow going over the control surfaces, especially at slower speeds. The XPWR 3910 also puts out about 1068 watts, which is about a 38% increase in power. If you want to build the ultimate MXS, this is the final piece you need.

Since the MXS has a wrapped balsa fuselage, it is a little heavier than the other EXPs, and you have to manage your speed and momentum a little better to get the most out of it. With a little more power that would not be the case, so it seems like a sure fire natural to retrofit one with an Xpwr 3910 and take advantage of that 1087 watts,

So, much like drivers of the street race cars on the show "Street Outlaws," I had to pick a cool name for the plane, so this will be the "Psycho Killer MXS."

Equipment

The Revolutionary Xpwr 3910 motor
The evolution, however, seems to have turned into a revolution. The world changed overnight with the simple release of a single item, which was the Xpwr 3910 motor. With the release of Extreme Flight's brutish Xpwr 3910 motor, the next great revolution is upon us. Certainly there will be new airframes designed around this fire breathing 1000 watt power plant, but the motor is here now and people are always crying for more power.

Now the full story can be revealed that the 3910 was designed for Extreme Flight's upcoming exciting new 52" Extra EXP, which we will be extensively reporting on soon. With the kind of investment Extreme Flight has made in this new motor, you can be sure there will be more 52" offerings, so you'de better hang on to your butt. It's going to be a wild ride!

You might not think a motor, no matter how good, would revolutionize the hobby, but the 3910 is merely a small window into the kind of things we can expect. You'll be seeing much more of that in the coming months, but let's stick with the 3910 and the MXS for now.

My Xpwr 3910 puts out a whopping 1068 watts at 73 amps on a Xoar 14/8 propeller and a Thunder Power 4s 2700 Magna 70C series battery. It's just crazy power for this sized plane, but it's certainly a lot of fun.

Since I have a house full of the current 48" EXPs, I recently fitted a 3910 to my beloved Extra EXP, and the transformation was beyond startling. Top speed was increased moderately, but the big gain is in barbaric punch out from hovers and harrier, and acceleration is absolutely blinding. Really, this power system blasts the Extra EXP into a totally different dimension and every single aspect of flight is greatly improved.

As such, I think any of the current 48" EXP lineup will benefit from using this motor. However, they won't be super gentle little putt-putt planes. I would say it's more like they will be a fire breathing monsters, but I've already used that and it doesn't really go far enough. The 3910 transforms a 48" EXP into a rabid demon.

Fitting the motor took a little bit of fiddling, but it was not a big deal. The hard part was figuring it all out, but I've already done that for you in Installing The Xpwr 3910 In A 48" EXP .

Hitec MH Servos
The MXS has always been a little bit of a psycho plane to begin with. With it's sort tail moment the MXS has always had great pitch authority, and is capable of insane violence. Snaps, spins and tumbles have always been crazy with this plane. With the advent of Hitec's excellent new HS5070MH and HS5087MH (for the elevator) servos, this aspect of the planes performance was greatly enhanced. So, to build the best MXS I know how, these servos were essential. I run them off a Castle Creations' 10 amp BEC .

Previously I was running these servos on 7.4 volts, but for the Extra EXP with Xpwr 3910 project I bumped them up to 8.0 volts and this improved the centering. The extra speed threw my timing off a little, but I just had to make a small adjustment to my flying and now I can take advantage of that.

Not being into specs and numbers, I almost never talk about specs and numbers, but for those of you who are, tech details for the 5070MH and 5087MH are listed below.

Specifications HS570MH

Motor Type:

3 Pole

Bearing Type:

Top Ball Bearing

Speed (6.0V/7.4V):

0.14 / 0.12 sec @ 60 deg.

Torque oz./in. (6.0V/7.4V):

42 / 52

Torque kg./cm. (6.0V/7.4V):

3.0 / 3.7

Size in Inches:

0.92 x 0.56 x 1.11

Size in Millimeters:

23.6 x 11.6 x 28.1

Weight ounces:

0.50

Weight grams:

14.2

Specifications HS5087MH

Motor Type:

3 Pole Ferrite

Bearing Type:

Top Ball Bearing Support

Speed (6.0V/7.4V):

0.17 / 0.13 second

Torque oz./in. (6.0V/7.4V):

50 / 60 oz-in

Torque kg./cm. (6.0V/7.4V):

3.6 / 4.3 kg-cm

Size in Inches:

1.14 x 0.51 x 1.18 in

Size in Millimeters:

29 x 13 x 30 mm

Weight oz.:

0.77 oz.

Weight g.:

21.9 g.

Servo And Control Linkage Set Up
The fortunate part of this project is that I already have an MXS set up with the HS5070MH and
HS5087MH (on elevator) servos. With these and the Xpwr 3910, this is as bad ass of an MXS as I know how to build. All that would be required would be retrofitting the plane to take a 3910.

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Here, I am going to cheat a little bit and use pictures I took of my servo set up for an earlier article, though it's still the same plane. These are identical to the set up pictures in the manual with the exception that I use a Hitec fiber filled arm from the PN55709 servo arm set. With this arm I get a full 88 degrees of elevator travel, which comes in handy for hard tumbling maneuvers, walls, parachutes and generally any time you want to rotate the plane hard. Coupled with the massive torque of the HS5087MH servo on the elevator, pitch authority is insane even at terminal velocity speeds.

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Special thanks to my friends at Hitec for providing the awesome servos for this project.

Mounting The Xpwr 3910 In The MXS
My RC Groups friend Cansfan from Arizona is a brilliant machinist, and he made up a mount for the 3910 that makes it a bolt on operation. Nice, simple, clean, and it will work on all the other 48" EXPs. We are working to make some more of these mounts, and as of this writing we are also working on distribution so the rest of you can enjoy this motor without having to modify your planes.

Here you can see how much smaller Cansfan had to make the mount to fit the firewall.

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The front side of the motor is stepped to make the entire assembly the same length as a 2814 with it's mount attached. This way, you just simply swap the motors out and your cowl spacing and alignment says the same.

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Also notice the holes in the rear of the mount are deeply countersunk. This way you bolt the motor to the mount using the bolts that came with the motor. To make this conversion all I needed was Scott's mount and the stuff that came in the box.

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As you can see, you simply bolt the thing on. The motor itself is so much bigger around than the bolt pattern on the firewall that you will need a good ball driver to secure the mount to the plane, but I just used a Dubro ball driver and it worked fine. On previous 3910 installations I had to discard the supplied mount, drill the firewall and rear mount the motor to the firewall itself. With the new mount, none of that is necessary. You just bolt it on the motor and then bolt the whole assembly to the firewall, just like you would do with the standard Torque 2814.

Mounting The Superb Airboss 80 ESC
I have been a huge fan of the Airboss 45 and 80 amp ESCs for as long as I can remember. In the 48" planes they have solved every problem I have ever encountered such as the need to be easy to program, to be 4s capable and having a 6 volt BEC. I have used these exclusively in all my planes for the last 10 years and have always had dead solid perfect throttle response and reliability. So, for this project there was never any other choice.

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I mounted the Airboss on the bottom of the motorbox where the manual says to put the Airboss 45. Since this unit is a little heavier than the Airboss 45 we usually use on this plane, I mounted it further back so the added weight would not affect the CG too much. As you can see, I used a block of balsa to raise the servo up enough to clear the first former, and then I could slide it back. This also works out well in moving the deans connector that goes to the battery back where it is easier to connect.

This puts the ESC just behind to intake snorkel on the bottom of the cowling and in plenty of onrushing cool air, which is essential when you are pumping out 73 amps. This frees up the two upper intakes to cool the motor, which is greatly helped by the cooling baffles that come with every EXP. The MXS has the smallest cooling intakes in the EXP lineup, so you have to make your installation as thermally efficient as possible.

Feeding The Servos
This project will be a little different in that I won't be relying on the Airboss' 6 volt BEC. We need 7.4 to 8.0 volts to feed the MH servos, so for this I use a Castle Creations' 10 amp BEC. These are easy to use with their Castle Link UBS programming cord. You download their Castle Link Program, plug everything together and simply select your BEC voltage. Even with my poor computer skills it was really easy. I've been using the Castle BEC on all of my 7.4 volt planes and they have worked flawlessly Generally I hate using a separate BEC because of the added complexity, but once I installed one or two I got used to it and it's no longer an issue. It's just part of what you have to do to build a bad ass airplane.
After soldering the leads from the Castle BEC to my deans plug, I simply used Velcro to place it low in the fuselage where it (and it's wires) would be out of the way when changing out the battery. I dislike the complication of BECs because it's hard to get a really clean installation once you start adding wires, but this was not so bad.

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Flying The Psycho Killer MXS

The world changed overnight. Literally.

With the extra grunt afforded by the Xpwr 3910's 1068 watt of power, the MXS becomes a totally different beast. I was not completely surprised since I had sampled this motor before in my Extra EXP, but I am still impressed with it. Every area of performance is enhanced, but let's break them down one by one.

Speed: Top speed is more, obviously, but not quite as much as I was expecting. These are still big airframess that generate lift from a lot of drag producing area. Nothing is free. To push past that, the faster you go the more the power requirement multiplies exponentially, and I did not take that into consideration. I certainly was not disappointed because the MXS was bordering on scary before and now it's just plain wicked. My best guess is that it's about 10-15 mph faster. Then again, that's just a guess. It's certainly enough of an increase to demand a bit more respect from the pilot, and probably terrifying for lesser experienced pilots.

Not only does the speed itself make the plane more locked in during precision flying, but we also have an additional 2" of thrust (airflow) coming off the 14/8 prop, and going over the airframe and control surfaces. This makes response crisp and precise, thus enhancing high speed smoothness, precision and agility. I had experienced this with the 3910 powered Extra EXP, but this improvement was worth mentioning again.

While we are talking about speed, now it's so serious that I emplore you to seal your hinge gaps and make your linkages as solid as you can. I did not experience any high speed flutter, but a plane prepared to less than the highest standards might, and that's certainly not covered under warranty.

As such, I recommend that you avoid full power downlines. I've done it when no one was around, just to be absolutely certain I have the safest plane I know how to build, but I try to avoid that when the field is crowded or the easily frightened are around.

Stunning. No amount of words can convey the way the plane simply disappears in a matter of seconds punching out of a hover, so check the video. If you have ever watched a football come off the foot of an NFL punter, that is what the MXS does when you hammer out out of a hover.

Vertical Pulling Power

With the vertical pulling power you can do loops and Cuban eights that are bigger than the flying field, and now at my smaller club I have to pay more attention to the airspace boundaries. If you like doing blenders and KE spins, or other falling type maneuvers, you get up there so fast that the time it takes is minimal enough that no one will lose interest.

In fact, initially I was having trouble setting up some maneuvers because under power the plane would climb so fast it would be too high before I could execute. Of course, it's the pilot's job to adapt, which I am still working on. At first it was hard to keep the plane on the deck simply because the motor would wrench the plane to altitude the moment you point the nose up. This is certainly not a complaint. It's just something you have to adapt to.

Acceleration

If you were to scale this plane up to full scale, the acceleration would make the pilot's head explode on the back of the canopy. At first, the plane was jumping out of harrier before I wanted it to, simply because I was not used to it's ability to generate speed from nothing. This is why a project like this is probably better for experienced pilots. If you are not careful the motor will make the plane jump out from under you. Just the acceleration alone is enough to make you second guess your own abilities.

The acceleration, is however, very useful once you learn to harness it. It's just plain fun to fly the aero equivalent of a top fuel dragster. Drop the hammer and it's like a pair of twin turbos kicking in. Come on.....it's just fun to see it rocket away like that.

From a near dead stop you can snap roll the plane really hard in a matter of seconds simply by accelerating to speed. That, and with more thrust going over the control surfaces from the bigger propeller, you can snap the plane harder with less actual ground speed.

Alpha Flight

This aspect of flight also changed as well. With so much grunt on hand you have to play your throttle with more finesse or the plane will jump right back onto it's wings and start flying again. I suppose it is already technically flying because so much air from the huge propeller is going over the plane, even when it's almost stopped, simply because of the large propeller.

Control response with the bigger propeller almost feels like you have more throw in the plane. If you are not careful setting up your hover with most planes, you can run out of ailerons to counter the torque, but with larger cone of thrust (airflow) coming off the prop, this stops being an issue.

Harrier is greatly improved because of not only improved airflow, but now you have the power to
hold the nose at a much higher angle, and simply rocket away if you stall the plane.

Nail
What we have done here is roughly equivalent to jamming a big V8 into a Volkswagen Beetle, so it's not going to be the same plane. This is a very advanced project and never intended for beginners. With the addition of the Xpwr 3910, now you'de better really know what you are doing. The Xpwr 3910 turns the MXS into such a serious 3DXA weapon that you need to stay on top of it. For experienced pilots, they know enough to adapt, but the newer guys are much better off with the easier handling of the standard 2814, which is already enough power to make the MXS one of the baddest planes around.

However, for those who are always looking for the extreme and want as much power as you can jam into the plane, I believe you will be much more than satisfied. Just remember that this is now a very serious airplane and to fly it responsibly.